Bee of the Month – Diadasia
Summer is upon us bringing heat to most of California and with it the Mallow-Loving Digger Bees (Diadasia spp.)! The genus Diadasia is represented by about 20 species in California, and we’ve recorded about 8 species in our urban survey work. These bees are mostly specialists or oligoleges, collecting pollen from certain plant families like Malvaceae (Sphaeralcea and Malacothamnus), Cactaceae (Opuntia), Convolvulaceae (Calystegia and Convolvulus) and Asteraceae (Helianthus). While these bees sip nectar from a variety of flowers, they are required to collect pollen from these specific plants, depending on what type of Diadasia they are.
These are small to medium-sized stout bees, some completely covered in velvety hairs. Their heads are not as broad as their abdomens and the top of their heads is rounded, a distinguishing character of this group. The females build nests, often in dense aggregations, where their nests can be easily seen due to the “turrets” they build above ground. The turrets are made from cemented soil particles and can be erect, angled, or horizontal above the soil. The nest site may be active for a few years and then they will move to a new location to help keep down parasites.
To encourage these bees into your garden you must have their favorite host plants. If you live in the desert, like Bishop or Palm Springs, try planting native Opuntia cactus to attract them. Native sunflowers (Helianthus annuus) are a favorite of Diadasia enavata, the sunflower chimney bee.